Field of the Invention
Embodiments of the invention relate to a thin film transistor array substrate and a method for manufacturing the same. More specifically, the embodiments of the invention relate to a thin film transistor array substrate and a method for manufacturing the same capable of improving characteristics of a thin film transistor by applying a voltage to a shielding pattern and performing a thermal process.
Discussion of the Related Art
The importance of flat panel displays is recently increasing with the growth of multimedia. Thus, various types of flat panel displays such as liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and organic light emitting diode (OLED) displays have been put to practical use. Among the flat panel displays, the OLED display has excellent characteristics including a fast response time of 1 ms or less, low power consumption, a self-emitting structure, etc. Hence, there is no problem in a viewing angle of the OLED display. As a result, the OLED display has been considered as a next generation display.
A method for driving a display device is classified into a passive matrix driving method and an active matrix driving method using thin film transistors. In the passive matrix driving method, an anode and a cathode are configured so that they are perpendicular to each other, and lines are selected, thereby driving the display device. On the other hand, in the active matrix driving method, the thin film transistors are respectively connected to pixel electrodes, and the display device is driven by the voltage held by a capacitance of a capacitor connected to a gate electrode of the thin film transistor.
In addition to basic characteristics of the thin film transistor including a mobility, a leakage current, etc., durability and electrical reliability required to maintain long lifespan are very important in the thin film transistor. An active layer of the thin film transistor is generally formed of amorphous silicon or polycrystalline silicon. Amorphous silicon has the advantage of a reduction in the manufacturing cost of the active layer through a simple formation process. However, it is difficult to secure the electrical reliability. Further, it is very difficult to apply polycrystalline silicon to a large area device because of a high process temperature, and the uniformity of polycrystalline silicon based on a crystallization type is not secured.
When the active layer is formed of oxide, an excellent mobility of the thin film transistor may be obtained even if the active layer is formed at a low temperature. Further, because changes in a resistance of the active layer increase depending on an amount of oxygen, it is very easy to obtain desired physical properties of the thin film transistor. Therefore, in recent, an interest in the application of the thin film transistor is greatly increasing. In particular, examples of oxide used in the active layer include zinc oxide (ZnO), indium zinc oxide (InZnO), and indium gallium zinc oxide (InGaZnO4).
However, because the thin film transistor including the active layer formed of oxide generates a light current by an external light source and thus shows unstable characteristic, the reliability of the thin film transistor is reduced.